At present, the semiconductor manufacturing industry develops rapidly under the guidance of Moore's law. It is needed to reduce the power consumption as much as possible while increasingly improving the performance and integration density of the integrated circuit. It is a focus of the future semiconductor manufacturing industry to fabricate ultra-short channel devices having high-performance and low-power consumption. After entering the 22-nanometer technical node, in order to overcome the above problems, a quasi-SOI source/drain device is employed to greatly reduce the leakage current and lower the power consumption of the device, which gradually gains wide attentions. However, the existing fabricating processes of the quasi-SOI source/drain device are limited to be performed on a silicon substrate material and not yet extended to the high-mobility semiconductor substrates such as germanium, Group III-V materials. Moreover, in the existing fabricating processes, a quasi-SOI isolation layer is formed via thermal oxidation. As a result, a high heat budget is caused and the fabricating process is complicated, thus it cannot be well applied to the large-scale integrated manufacturing.